Steam engine safety valve. Safety valves with pressure control setting Steam safety valve
The safety valve is an essential part of a steam engine. Especially for a stranger where there are no measuring instruments or tools. Therefore, in order not to learn to fly, before the first start of the steam engine you need to take care of testing the steam valve. In general, the safety valve is the only part of a steam engine that must be constantly in working order.
Until the beginning of the 19th century, a steam boiler explosion was a fairly common occurrence. At that time, thermodynamics was poorly understood, and the materials were not so great. In order not to be nailed by his own steam engine, the victim needs to create a working safety valve that relieves pressure in the boiler if something happens.
There are few requirements for the valve. The main thing is reliability. Therefore, there is no need to be clever with the design. There were even valves with electromagnetic control that opened on command - but there was always a classic spring valve in parallel with such a valve.
And that’s why - no work with a file, everything should be processed on lathe with the required accuracy. And there should not be any crushable materials (such as asbestos). Only steel, only hardcore. Well, or copper, although a steel spring is still required.
The next requirement is to ensure the design throughput. Why do you need a valve that, when opened, the pressure still continues to increase?
And lastly, the valve must be installed outside the room where people are. In a steam locomotive he is always on the roof, in a steamship he is brought out onto the deck, even in factories he was taken higher and beyond indoors. Otherwise, as soon as it works, it will be difficult to even run out of the workshop; the fog turns out to be worse than that of “Hedgehog in the Fog.”
The design of all is quite simple - the steam pressure must overpower the spring and open the valve itself. The key element here is the spring, but the design is such that if the spring breaks, steam will escape and the boiler will not explode.
I'll just show you the drawings.
Here are domestic valves:
And here are the American ones from 1910:
Actually, this article is written not so much about a technical detail, but about a detail that requires special attention.
Moreover, when the purpose of the valve becomes known to the locals, it is a potential part for sabotage. And since it will be located outside...
In general - attention, and attention again!
STATE STANDARD OF THE USSR UNION
SAFETY VALVES
STEAM AND WATER BOILERS
TECHNICAL REQUIREMENTS
GOST 24570-81
(ST SEV 1711-79)
USSR STATE COMMITTEE ON STANDARDS
STATE STANDARD OF THE USSR UNION
|
SAFETY VALVES FOR STEAM AND WATER BOILERS Technicalrequirements Safety valves of stream and hot-water boilers. |
GOST (ST SEV 1711-79) |
By Decree of the USSR State Committee on Standards dated January 30, 1981 No. 363, the introduction date was established
from 01.12.1981
Verified in 1986. By Decree of the State Standard of June 24, 1986 No. 1714, the validity period was extended
until 01.01.92
Failure to comply with the standard is punishable by law
This standard applies to safety valves installed on steam boilers with absolute pressure above 0.17 MPa (1.7 kgf/cm2) and hot water boilers with water temperatures above 388 K (115 ° WITH).
The standard fully complies with ST SEV 1711-79.
The standard establishes mandatory requirements.
1. GENERAL REQUIREMENTS
1.1. To protect boilers, safety valves and their auxiliary devices are allowed that meet the requirements of the “Rules for the design and safe operation of steam and water-heating boilers” approved by the USSR State Mining and Technical Supervision.
(Changed edition, Amendment No. 1).
1.2. The design and materials of the elements of safety valves and their auxiliary devices must be selected depending on the parameters of the working environment and ensure reliability and correct operation under operating conditions.
1.3. Safety valves must be designed and adjusted so that the pressure in the boiler does not exceed working pressure by more than 10%. An increase in pressure is allowed if this is provided for in the boiler strength calculations.
1.4. The design of the safety valve must ensure free movement of the moving elements of the valve and exclude the possibility of their release.
1.5. The design of safety valves and their auxiliary elements must exclude the possibility of arbitrary changes in their adjustment.
1.6. Each safety valve or, by agreement between the manufacturer and the consumer, a group of identical valves intended for one consumer, must be accompanied by a passport and operating instructions. The passport must comply with the requirements of GOST 2.601-68. The section “Basic technical data and characteristics” should contain the following data:
name of the manufacturer or its trademark;
year of manufacture;
valve type;
nominal diameter at the inlet and outlet of the valve;
design diameter;
calculated cross-sectional area;
type of environment and its parameters;
characteristics and dimensions of the spring or load;
steam consumption coefficienta , equal to 0.9 coefficient obtained on the basis of tests;
permissible back pressure;
opening start pressure value and permissible opening start pressure range;
characteristics of the materials of the main elements of the valve (body, disc, seat, spring);
valve type test data;
catalog code;
conditional pressure;
permissible operating pressure limits for the spring.
1.7. The following information must be marked on a plate attached to the body of each safety valve, or directly on its body:
name of the manufacturer or its trademark;
serial number according to the manufacturer's numbering system or series number;
year of manufacture;
valve type;
design diameter;
steam consumption coefficienta;
opening start pressure value;
conditional pressure;
nominal diameter;
flow indicator arrow;
body material for fittings made of steel with special requirements;
designation of the main design document and symbol of the product.
The location of the marking and the size of the markings are established in technical documentation manufacturer.
1.6, 1.7.(Changed edition, Change № 1).
2. REQUIREMENTS FOR DIRECT ACTING SAFETY VALVES
2.1. The design of the safety valve must include a device for checking the proper operation of the valve during boiler operation by forcing the valve to open.
The possibility of forced opening must be ensured at 80% of the opening pressure.
2.1.
2.2. The pressure difference between full opening and the beginning of opening of the valve should not exceed the following values:
15% of the opening start pressure - for boilers with an operating pressure not higher than 0.25 MPa (2.5 kgf/cm 2);
10% of the opening pressure - for boilers with operating pressure above 0.25 MPa (2.5 kgf/cm2).
2.3. Safety valve springs must be protected from unacceptable heat and direct exposure to the working environment.
When the valve is fully opened, the possibility of mutual contact of the spring coils must be excluded.
Design spring valves should exclude the possibility of tightening the springs beyond the set value due to the highest operating pressure for a given valve design.
2.3. (Changed edition, Amendment No. 2).
2.4. The use of valve stem seals is not permitted.
2.5. In the safety valve body, in places where condensate may accumulate, a device must be provided for its removal.
2.6. (Excluded , Change No. 2).
3. REQUIREMENTS FOR SAFETY VALVES CONTROLLED BY AUXILIARY DEVICES
3.1. The design of the safety valve and auxiliary devices must exclude the possibility of unacceptable shocks when opening and closing.
3.2. The design of safety valves must ensure that the function of protection against overpressure is maintained in the event of failure of any control or regulating body of the boiler.
3.3. Electrically driven safety valves must be equipped with two power sources independent of each other.
IN electrical diagrams, where the disappearance of energy causes a pulse to open the valve, a single source of electrical power is allowed.
3.4. The design of the safety valve must provide for the ability to control it manually and in necessary cases remote control.
3.5. The valve design must ensure that it closes at a pressure of at least 95% of the operating pressure in the boiler.
3.6. The diameter of the straight-through pulse valve must be at least 15 mm.
The internal diameter of the impulse lines (input and outlet) must be at least 20 mm and not less than the diameter of the output fitting of the impulse valve.
Impulse and control lines must have condensate drainage devices.
The installation of shut-off devices on these lines is not permitted.
It is allowed to install a switching device if, in any position of this device impulse line will remain open.
3.7. For safety valves controlled by auxiliary impulse valves, it is possible to install more than one impulse valve.
3.8. Safety valves must be operated in conditions that do not allow freezing, coking and corrosive effects of the environment used to control the valve.
3.9. When using an external power source for auxiliary devices, the safety valve must be equipped with at least two independently operating control circuits so that if one of the control circuits fails, the other circuit ensures reliable operation of the safety valve.
4. REQUIREMENTS FOR SUPPLY AND DISCHARGE PIPELINES OF SAFETY VALVES
4.1. It is not allowed to install shut-off devices on the inlet and outlet pipelines of safety valves.
4.2. The design of safety valve pipelines must provide the necessary compensation for temperature expansion.
The fastening of the body and pipelines of safety valves must be designed taking into account static loads and dynamic forces that arise when the safety valve is activated.
4.3. The supply pipelines of the safety valves must have a slope along their entire length towards the boiler. In the supply pipelines, sudden changes in wall temperature should be excluded when the safety valve is activated.
4.4. The pressure drop in the supply pipeline to direct-acting valves should not exceed 3% of the pressure at which the safety valve begins to open. In the supply pipelines of safety valves controlled by auxiliary devices, the pressure drop should not exceed 15%.
When calculating the valve capacity, the indicated pressure reduction in both cases is taken into account.
4.4. (Changed edition, Amendment No. 2).
4.5. The working medium must be drained from the safety valves to a safe place.
4.6. Discharge pipelines must be protected from freezing and have a device for draining condensate.
Installation of shut-off devices on drains is not permitted.
4.6.(Changed edition, Amendment No. 2).
4.7. The internal diameter of the outlet pipe must be no less than the largest internal diameter of the outlet pipe of the safety valve.
4.8. The internal diameter of the outlet pipe must be designed so that at a flow rate equal to the maximum capacity of the safety valve, the back pressure in its outlet pipe does not exceed the maximum back pressure established by the safety valve manufacturer.
4.9. The capacity of safety valves should be determined taking into account the resistance of the sound muffler; its installation should not cause disruption to the normal operation of safety valves.
4.10. A fitting must be provided in the area between the safety valve and the sound muffler for installing a pressure measuring device.
5. FLOW CAPACITY OF SAFETY VALVES
5.1. The total capacity of all safety valves installed on the boiler must satisfy the following conditions:
for steam boilers
G1+G2+…Gn³ D;
for economizers disconnected from the boiler
for hot water boilers
n- number of safety valves;
G1,G2,Gn- capacity of individual safety valves, kg/h;
D- rated output of the steam boiler, kg/h;
Increase in enthalpy of water in the economizer at the nominal boiler output, J/kg (kcal/kg);
Q- nominal thermal conductivity of the hot water boiler, J/h (kcal/h);
g- heat of evaporation, J/kg (kcal/kg).
Calculation of the capacity of safety valves of hot water boilers and economizers can be carried out taking into account the ratio of steam and water in the steam-water mixture passing through the safety valve when it is activated.
5.1. (Changed edition, Amendment No. 2).
5.2. The capacity of the safety valve is determined by the formula:
G = 10B 1 × a× F(P 1 +0.1) - for pressure in MPa or
G= B 1 × a× F(P 1 + 1) - for pressure in kgf/cm 2,
Where G- valve capacity, kg/h;
F- design cross-sectional area of the valve, equal to smallest area free cross-section in the flow part, mm 2 ;
a- steam flow coefficient, related to the cross-sectional area of the valve and determined in accordance with clause 5.3 of this standard;
R 1 - maximum overpressure in front of the safety valve, which should be no more than 1.1 working pressure, MPa (kgf/cm2);
IN 1 - coefficient taking into account physical and chemical properties steam at operating parameters in front of the safety valve. The value of this coefficient is selected according to the table. 1 and 2.
Table 1
Coefficient values IN 1 for saturated steam
|
R 1, MPa (kgf/cm2) |
|||||||
|
R 1, MPa (kgf/cm2) |
|||||||
|
R 1, MPa (kgf/cm2) |
|||||||
Table 2
Coefficient values IN 1 for superheated steam
|
R 1, MPa (kgf/cm2) |
At steam temperaturetn, ° WITH |
||||||||
|
0,2 (2) |
0,480 |
0,455 |
0,440 |
0,420 |
0,405 |
0,390 |
0,380 |
0,365 |
0,355 |
|
1 (10) |
0,490 |
0,460 |
0,440 |
0,420 |
0,405 |
0,390 |
0,380 |
0,365 |
0,355 |
|
2 (20) |
0,495 |
0,465 |
0,445 |
0,425 |
0,410 |
0,390 |
0,380 |
0,365 |
0,355 |
|
3 (30) |
0,505 |
0,475 |
0,450 |
0,425 |
0,410 |
0,395 |
0,380 |
0,365 |
0,355 |
|
4 (40) |
0,520 |
0,485 |
0,455 |
0,430 |
0,410 |
0,400 |
0,380 |
0,365 |
0,355 |
|
6 (60) |
0,500 |
0,460 |
0,435 |
0,415 |
0,400 |
0,385 |
0,370 |
0,360 |
|
|
8 (80) |
0,570 |
0,475 |
0,445 |
0,420 |
0,400 |
0,385 |
0,370 |
0,360 |
|
|
16 (160) |
0,490 |
0,450 |
0,425 |
0,405 |
0,390 |
0,375 |
0,360 |
||
|
18 (180) |
0,480 |
0,440 |
0,415 |
0,400 |
0,380 |
0,365 |
|||
|
20 (200) |
0,525 |
0,460 |
0,430 |
0,405 |
0,385 |
0,370 |
|||
|
25 (250) |
0,490 |
0,445 |
0,415 |
0,390 |
0,375 |
||||
|
30 (300) |
0,520 |
0,460 |
0,425 |
0,400 |
0,380 |
||||
|
35 (350) |
0,560 |
0,475 |
0,435 |
0,405 |
0,380 |
||||
|
40 (400) |
0,610 |
0,495 |
0,445 |
0,415 |
0,380 |
||||
or determined by the formula for pressure in MPa
for pressure in kgf/cm 2
Where TO- adiabatic index equal to 1.35 for saturated steam, 1.31 for superheated steam;
R 1 - maximum excess pressure in front of the safety valve, MPa;
V 1 - specific volume of steam in front of the safety valve, m 3 /kg.
The formula for determining valve capacity should only be used if: ( R 2 +0,1)£ (R 1 +0,1)b kr for pressure in MPa or ( R 2 +1)£ (R 1 +1)b kr for pressure in kgf/cm 2, where
R 2 - maximum excess pressure behind the safety valve in the space into which steam flows from the boiler (when escaping into the atmosphere R 2 = 0 MPa (kgf/cm2);
b kr - critical pressure ratio.
For saturated steam b kr =0.577, for superheated steam b cr =0.546.
5.2. (Changed edition, Amendment No. 2).
5.3. Coefficient a taken equal to 90% of the value obtained by the manufacturer based on the tests performed.
6. CONTROL METHODS
6.1. All safety valves must be tested for strength, tightness, and tightness of gland connections and sealing surfaces.
6.2. The scope of valve testing, their order and control methods must be established in the technical specifications for valves of a specific standard size.
Sometimes unpleasant circumstances arise when the heating system malfunctions and the pressure begins to fluctuate. If the pressure is not regulated, the consequences can be dangerous. To prevent this from happening, heating system and feeding system hot water should be equipped with safety valves. What they are and how they work – we will tell you in this material.
Safety valve in the heating system performs protective function in order to prevent high pressure. This is especially important for steam boilers.
Blood pressure rises most often due to the following reasons:
- refusal automatic systems pressure adjustment;
- sudden increase in temperature environment and the appearance of steam.
Safety products are mainly of two types:
- spring;
- lever-load.
In lever-load structures, the action of pressure on the spool is counteracted by a load, its force is transmitted through the lever to the rod. It moves along the length of the lever, and in this way you can adjust the force of pressure of the spool against the seat. Then it opens when the working medium begins to press on the lower part of the spool with a force greater than the force of the lever pressure and the water leaves through the pipe.
And the spring safety units work by using electromagnetic drive . A spring exerts pressure on the spool rod, and adjustment occurs by changing the degree of compression of the spring.
Small heating systems are best combined with spring products; their advantages in this case are as follows:
- compactness;
- the setting can only be changed when using the tools;
- the spool rod may have different positions;
- Possibility of combination with other products.
According to the principle of operation, safety valves are divided into the following:
Safety valve direct action can open only under pressure from the working medium, indirectly - under the influence of a pressure source.
And according to the type of lifting the constipation, the devices are:
- low-lift;
- medium-lift;
- full lift.
Manufacturing materials
Safety products can be made from the following materials:
- brass;
- steel;
- galvanized steel;
- stainless steel
Features of the mechanism and design
The safety brass coupling valve for the boiler is threaded on both sides and has a gasket on the inlet side. The mechanism is spring-loaded. External pressure can increase the blockage. After assembling the structure, it is pressurized, so this type of valve is very reliable and affordable.
Safety shut-off valve also can work in sewer system to protect against backflow pressure.
Features of three-way valves
The purpose and operating principle of three-way safety valves is somewhat different from other options, and so their key differences:
Such valves are most often used in heating systems that include “warm floors”. In this way, the water for heating the floors will be much cooler than the water in the radiator.
For the manufacture of three-way safety valves the following is used:
- steel;
- brass;
- cast iron.
Brass structures are most common when installing home heating systems, while steel and cast iron are more typical for larger industrial installations.
It is also worth paying attention to the explosion safety valve, which can prevent the explosion of flammable gases or coal dust. They are made in such a way that if the substance explodes, only the membrane of the structure is damaged, and the pipeline remains unharmed.
This type of product operates automatically. Depending on the pressure, their There are several types of them:
- with pressure up to 2 kPa;
- up to 40 kPa;
- 150 kPa inclusive.
How to choose the right safety valve
When choosing a safety valve, you should consider huge amount certain factors. In particular, be sure to take the ambient operating pressure into account. If this pressure is higher than normal, then you need choose a product for 2 bar, which can withstand such operating conditions of the product. In addition, you can choose an option with the ability to adjust the pressure so that you can adjust the required mode and find out the exact parameters, in particular, the nominal diameter.
There are a number of standards regarding the performance of calculations; you can also find special calculation programs on the Internet. You can do without calculations and take a structure with a diameter no less than the diameter of the outlet pipe of your boiler, but such a calculation will not be accurate and cannot guarantee high level safety and productivity.
In general, in order to choose the right product, you should consider the following parameters:
- decide on the type of product;
- with a size so that the pressure in the system does not exceed the permissible limits;
- It is better to choose spring-type products for your home;
- open devices are suitable only if the water goes into the atmosphere, and closed ones - if into the outlet pipeline;
- after calculations, you can determine whether a low-lift valve or a full-lift valve is suitable;
- calculate your budget.
Safety valve prices vary depending on the material and other features. For example, an Italian-made membrane structure can be buy for about 4 USD., and brass – starting from 12 USD. There are also some valve models whose cost exceeds $100.
Safety valve installation features
When installing the valve, you must strictly follow all the rules that are listed in the regulatory documentation of the product. Also, the installation must be carried out taking into account the power and operating pressure.
But The key installation principles are:
We also must not forget that it is necessary to regulate and check the pressure at least once a year before the heating season.
How to set a safety valve
The valve must be adjusted at the installation location after completion installation work and after the system is flushed. Set the setting pressure, check the opening and closing pressure of the product.
The settings should be set slightly above the maximum operating pressure, which is permissible during normal operation of the structure. A full opening pressure should not be higher than the minimum level of the weakest element of the system. The closing pressure must exceed the minimum permissible value.
Adjust the pressure in spring design it is necessary by rotating a special screw that compresses the spring, and the lever structure is adjusted using the required mass of the load.
So, the valve is ready for operation, if he is able to ensure the tightness of the overlap, as well as the complete opening and closing of the shutter. In addition, the pressure may deviate within the permissible fluctuations, which are given in the technical data sheet of the product.
Today, the range of steam fittings is represented by dozens of types various devices. The mechanisms differ in design, as well as a set of other parameters:
- body material. The devices used in steam circulation systems are usually made of ductile iron, ductile iron or galvanized steel. stainless steel, as well as brass and other metals. Depending on the principle of operation of the mechanism, its design may also contain various seals made from special types of rubber that are resistant to high temperatures;
- management principle. Many types of such equipment have simple manual control, carried out using a gearbox or other mechanisms. IN modern systems In heating systems, automated devices are increasingly being used, the operation of which is ensured by an electric drive. Some mechanisms function autonomously;
- connection type. In steam circulation systems, as a rule, high blood pressure. Given this fact, the fittings used in them rarely have a threaded connection, since it does not provide adequate reliability. Typically, a steam system uses mechanisms that are connected using flanges or welding.
Range of steam equipment
Modern heating systems use various types steam fittings, each of which has its own characteristics and purpose.
- Steam traps. This type of equipment provides automatic removal of water generated during heat exchange between media or during heating of the pipeline system, which causes steam to transform into liquid.
- Condensate pumps. The task of these steam fittings is to pump a vaporous medium in the event of a lack of electricity. The condensate temperature is allowed to exceed the level established for centrifugal pumps.
- Safety valves. Such fittings ensure the release of excess steam or other working fluid through the nozzles in order to protect the pipeline, boiler equipment, containers and other elements from damage by high pressure.
- Shut-off and control valves. This type of steam fitting provides control certain parameters working environment. For example, it can be used to control and change the concentration, temperature, pressure or flow of substances in any section of the pipeline.
- Check valves. Such fittings perform, first of all, a protective function. Design features allow it to prevent the formation of reverse steam flow in the pipes, which can lead to an accident in the heating system.
- Ball valves. This type of steam fittings is used to block the flow of the working medium in certain areas of the system. As a rule, the device operates only in two modes, providing for complete closing or opening.
